Lower first permanent molars: developing better predictors of spontaneous space closure.

BACKGROUND: First, first permanent molars (FPMs) of poor prognosis are often planned for extraction at an 'ideal time' so that second permanent molars (SPMs) erupt favourably to replace them. However for lower FPM extractions, timing is not an accurate predictor of success. OBJECTIVE: The aim of this study was to identify additional radiographic factors that could better predict the degree of spontaneous space closure of the lower SPM following FPM extraction. METHODS: Data from a previous study of 127 lower SPMs from 66 patients was re-analysed by incorporating additional radiographic factors. These included calcification stage of the bifurcation of the SPM, position of the second premolar, mesial angulation of SPM in relation to the FPM, and presence of the third permanent molar. Results were analysed using ordered logistic regression. RESULTS: Only 58 per cent of FPMs extracted at the 'ideal time' (SPM development at Demirjian stage E) had complete space closure. The best outcomes resulted from a combination of SPMs not at Demirjian development stage G, together with the presence of mesial angulation of the SPM and presence of the third permanent molar, where 85 per cent of those cases had complete space closure. CONCLUSIONS: Apart from extraction timing of the FPM, consideration must also be given to the presence of the third permanent molar and angulation of the SPM in order to ensure a reliable degree of spontaneous space closure of the lower SPM.

Physiological distal drift in rat molars contributes to acellular cementum formation.

Occlusal forces may induce the physiological teeth migration in humans, but there is little direct evidence. Rat molars are known to migrate distally during aging, possibly caused by occlusal forces. The purpose of this study was to determine if a reduction in occlusion would decrease teeth migration and affect associated periodontal structures such as cementum. To reduce occlusal forces, the right upper first molar (M1) in juvenile rats was extracted. The transition of the position of upper second molar (M2) and formation of M2 cementum was followed during aging. From the cephalometric analyses, upper M2 was located more anterior compared with the original position with aging after M1 extraction. Associated with this "slowing-down" of the physiological drift, cementum thickness on distal surface, but not on mesial surface, of M2 root was significantly increased. The accumulation of alizarin red as vital stain indicative of calcification, was observed in the distal cementum of M2 root only on the side of M1 extraction. Extraction of M1 that results in less functional loading, distinctly attenuates the physiological drift only in the upper dentition. The decreased physiological drift appears to activate acellular cementum formation only on distal surface of M2 root, perhaps due to reduced mechanical stress associated with the attenuated distal drift. In conclusion, the physiological distal drift in rat molars appears to be largely driven by the occlusal force and also affects the formation of acellular cementum. These findings provide additional direct evidence for an important role of occlusal forces in tooth migration.

Lifelong craniofacial growth and the implications for osseointegrated implants.

PURPOSE: The sequence of observations presented is intended to alert the dental profession to complications that may occur when teeth and implants co-exist and subtle adult craniofacial growth occurs. MATERIALS AND METHODS: The authors' observations of partially edentulous implant restorations with more than 20 years of follow-up included some observed changes relative to patients' remaining teeth and jaw structures. These changes, which were not easily explained and appeared to be random deviations from expected implant-restorative stability, conformed with research findings of craniofacial growth continuing into adulthood. The authors identified several distinct areas in which such adult craniofacial growth could potentially influence the relationship of implant restorations to the remaining teeth and jaw structure. RESULTS: Potential esthetic, occlusal, and periodontal ramifications of continued adult craniofacial growth were found to include changes in occlusion, opened contact as a result of teeth migration, and changes in anterior esthetic results. The latter may include labialization of the anterior implant restoration and a progressive discrepancy of the cervical gingival margin of the implant restoration relative to the adjacent teeth. Cases are presented showing poor sequellae of treatment due to growth occurring after the assumption was made that a stable jaw dimension had been reached. While continued adult craniofacial growth sufficient to cause clinical problems is not common, it is also presently not predictable. CONCLUSION: When changes in tooth position relative to implant restorations secondary to long-term adult growth occur, they can cause problems that are difficult or even impossible to correct. Future research will ideally enable identification of patients at risk for developing such problems.

[Three-dimension model analysis for physiological drift of the mandibular dentition after extraction of mandibular second premolars of Angle class II patients].

OBJECTIVE: To observe the self-adjustment of the mandibular dental arch after extraction of the second mandibular premolars. METHODS: Mandibular dental casts of 20 Angle class II patients treated with extraction of lower second premolars and upper first premolars, bonded with Alexander appliance,were taken before (T1) and after self-adjustment (T2). All the casts were laser scanned, Little index, curve of Spee, arch width, arch length and extraction spaces of casts were digitally measured and analyzed with SPSS 16.0. RESULTS: Little index,lower molar width, lower arch length and extraction spaces were reduced [(12.70±3.28) mm vs.(8.82±2.69) mm, P<0.001;(41.21±2.48) mm vs.(40.54±2.23) mm, P<0.001; (24.63±3.19) mm vs.(22.12±2.97) mm, P<0.001;(8.06±0.48) mm vs.(4.17±1.51) mm, P<0.001;(8.13±0.95) mm vs.(4.14±1.98) mm, P<0.001],while the curve of Spee and anterior lower arch length were increased significantly[(2.14±0.75) mm vs.(2.65±0.88) mm, P<0.05; (15.88±2.86) mm vs.(17.55±2.33) mm, P<0.05]. Width between lower canines remained the same[(27.25±2.69) mm vs.(27.26±1.73) mm, P>0 .05]. CONCLUSION: Severe crowding and Angle class II molar relationship could be successfully relived with lower second premolar extraction followed by self-adjustment.

Material properties of periodontal ligaments.

The mechanism of orthodontic teeth movement is not entirely explained. The principal reaction on tissues at the cellular and molecular level is initiated by the force applied to the tooth crown and transferred in turn upon the periodontal ligament (PDL). It seems, therefore, that the PDL and particularly its properties play a key role in bone remodelling. One of the more commonly used methods, which is capable of analysis of a wide range of orthodontic movements or distribution of stress and strain within teeth and periodontium, is the finite element method (FEM). Aiming to achieve the FEM model as close as possible to in vivo conditions, it is necessary to account for accurate material properties. The aim of the present study is to compare particular studies and descriptions of material characteristics of the PDL. The analysis of available articles shows how imperfect modern descriptions of PDL material properties available today are, which in the precise method could allow the analysis of the occurrences within the in vivo processes in a non-destructive manner. The complicated anatomy and physiology of PDL, which incur significant parameter changes with age and disease susceptibility, make the accurate description of this material so difficult. The available study results show that those characteristics should be precise and complicated, which undoubtedly impedes the calculation processes but generates reliable results.

Finite element analysis suggests functional bone strain accounts for continuous post-eruptive emergence of teeth.

OBJECTIVE: To explore the possible role of functional stress in driving continuous post-eruptive emergence of teeth. DESIGN: A two dimensional finite element analysis model was established with a single mandibular premolar subjected to sagittal bending. Equivalent strain was charted for the inner and outer surfaces of the lamina dura, because bone deposition and resorption of this structure is confined to surface osteoblasts and osteoclasts. Bone disuse resorption was assumed to take place at equivalent strain values below 0.0008, while deposition was above 0.002. Strain in the periodontal ligament and principal stress throughout the model were also characterized. RESULTS: Strain analysis indicated bone maintenance for the lamina dura throughout most of the root length, but in both the apical and upper root regions, resorption was predicted for the outer surface, and bone deposition was predicted for the inner surface of the lamina dura. Strain in the periodontal ligament varied little with the exception of a marked increase close to the crown. Principal stress analysis revealed compression of the lower model border, with areas of increasing tension towards the upper model border. CONCLUSIONS: Strain from functional forces may continuously drive post-eruptive emergence of teeth through bony remodelling of the lamina dura, lifting teeth by both raising the apical lamina dura, and narrowing the upper root space to accommodate tapering root form. Such strain-driven bone turnover may contribute to pre-eruptive movement of teeth.

First case of bimaxillary transmigration of impactedcanines: report of a rare case and review of literature / Primeiro caso de transmigração bimaxilar de caninosimpactados: relato de um caso raro e revisão da literatura

Objective: To present a rare case of bimaxillary transmigration of impacted canines. Discussion: Preeruptivemigration of a tooth across the midline is termed transmigration. Transmigration typically affectsthe mandibular canines, but occurs rarely in maxillary canines as well. Transmigration of mandibular canineacross the midline is rare. An even less common finding is transmigration of maxillary canine acrossthe midline. The least common finding is bimaxillary occurrence of canines transmigration. Conclusion:Migration of both upper and lower canine teeth on the same side across the midline is called bimaxillarytransmigration, which is a very rare phenomenon of oral and maxillofacial complex, often undetected inroutine dental examination, neither clinical, nor periapical radiographic examination.

Objetivo: Apresentar um caso raro de transmigração bimaxilar de caninos impactados. Discussão: A migraçãopré-eruptiva de um dente através da linha média é denominado transmigração. A transmigraçãotipicamente afeta os caninos inferiores, mas pode ocorrer raramente em caninos superiores também. Transmigraçãode canino inferior através da linha média é rara, porém um achado ainda menos comum é a ocorrênciade transmigração bimaxilar de caninos. Conclusão: A migração de caninos superiores e inferiores nomesmo lado e cruzando a linha média é chamada de transmigração bimaxilar, um fenômeno raro de sistema bucal e maxilofacial, frequentemente diagnosticado em exame clínico odontológico de rotina ou exame radiográficoperiapical.

Changes in molar position associated with missing opposed and/or adjacent tooth: a 12-year study in women.

The aim of this study was to radiographically analyse long-term changes in (i) overeruption of unopposed molars and (ii) tipping of molars with a mesial edentulous space, and whether there is an interaction between the two events. A further aim was to analyse if loss of alveolar bone height might influence overeruption and tipping. The sample consisted of panoramic radiographs taken at an interval of 12 years of 292 subjects from a prospective population study of women. The panoramic radiographs were scanned and analysed. Changes in tipping, overeruption and alveolar bone height of molars and control teeth were measured. The results showed that unopposed molars were more commonly found in the upper jaw and that unopposed molars showed 4·9 times higher risk of overeruption of ≥2 mm (95% CI 1·5-15·3) than opposed molars during the 12-year observation period. The average overeruption for the unopposed molars was 4·5% (s.d. 7·6), which corresponds to approximately 0·9 mm. The degree of overeruption increased with decreased bone support. Molars with a mesial edentulous space were most prevalent in the lower jaw, but neither an edentulous space nor alveolar bone level/bone level change were found to have a significant effect on tipping of the molars. The average mesial tipping was 0·8° (s.d. 5·6). In conclusion, unopposed molars showed a significantly increased risk for overeruption. Molars facing a mesial edentulous space showed a low risk for mesial tipping, but a significant interaction between overeruption and tipping was identified.

How does tooth eruption relate to vertical mandibular growth displacement?

INTRODUCTION: Our objectives were to investigate the eruptive patterns of the mandibular teeth and assess their associations with mandibular growth displacements. METHODS: Cephalograms for a mixed-longitudinal sample of 124 French-Canadian girls were evaluated between 10 and 15 years of age. Vertical mandibular displacement and mandibular eruption were evaluated by using cranial and mandibular superimpositions, respectively. Multilevel modeling procedures were used to estimate each subject's growth change over time. Stepwise multiple regressions were used to determine the amount and relative magnitudes of variations in mandibular eruption explained by mandibular growth displacement, controlling for vertical maxillary tooth movements. RESULTS: Cubic polynomial models explained between 91% and 98% of the variations in eruption and vertical growth displacement. All curves showed acceleration of eruption until approximately 12 years of age, after which eruption decelerated. The eruption of the mandibular teeth demonstrated greater relative variability than did vertical mandibular growth displacements. Independent of the overall movements of the maxillary molars, inferior mandibular growth displacement explained approximately 54% of the variation in mandibular molar eruption between 10.5 and 14.5 years of age. CONCLUSIONS: Inferior mandibular growth displacement and dental eruption followed similar patterns of change during adolescence. Based on their associations and the differences in variability identified, mandibular eruption appears to compensate for or adapt to growth displacements.

Analysis of different type of transmigrant mandibular teeth

Objective: Until recently, most reports about transmigration have documented that the canine is the only toothwhich can migrate to the opposite side of the arch. The goal of the study was to define the transmigration of differenttypes of teeth in people in various regions of Turkey.Study Design: A total of 112,873 panoramic radiographic files from seven different Turkish cities were inspected.The following data were evaluated according to age, gender, number of transmigrant teeth, localization, eruptionstatus, side, unilaterally or bilaterally and associated pathology or dental abnormalities.Results: Of the 112,873 radiographs included in the study, 90 were seen to present as transmigrant in 87 patients,representing 0.079% of the sample. There were only two (0.0017 %) transmigrant lateral (TML) teeth and onlythree (0.0026%) transmigrant premolar (TMP) teeth encountered. The mean age at the time that the transmigrantmandibular teeth were identified was 29.9 years, with a range from 10 to 66 years. Out of the 87 cases, 51 werefemale and 36 were male, with a male:female ratio of 1:1.41. Transmigrants were more commonly seen unilaterally(96.5%). The most frequent associated pathology was odontoma.Conclusions: Because early detection is vital to prevent complications and ensure more successful treatment, theseextensive studies are crucial. In this extensive study, we indicated cases of transmigration of premolar and lateralteeth as a variant. Demographic variables and properties of all transmigrants (TM) were also presented (AU)

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Osteopontin is required for unloading-induced osteoclast recruitment and modulation of RANKL expression during tooth drift-associated bone remodeling, but not for super-eruption.

Unloading of teeth results in extensive alveolar bone remodeling, causing teeth to move in both vertical ("super-eruption") and horizontal direction ("drift"). In order to decipher the molecular mechanisms of unloading-induced bone remodeling during tooth movement, we focused on the role of osteopontin (OPN) in the un-opposed molar model, comparing wild-type (WT) and OPN-null mice. Our data indicated that OPN was not required for the continuous eruption of un-opposed teeth while OPN was necessary for the drift of teeth. OPN expression and osteoclast counts were greatly increased on alveolar bone surfaces facing the direction of the drift in WT mice, while osteoclast counts were diminished in OPN-/- mice. RANKL expression in the distal periodontal ligament of WT molars increased significantly by day 6 following unloading, while overall levels of RANKL expression were decreased in both WT and OPN-null mice. In vitro treatment of MC3T3 cells, WT BMCs and OPN-/- BMCs with recombinant OPN resulted in significantly increased RANKL expression in all three cell types. The PI3K and MEK/ERK pathway inhibitors Ly294002 and U0126 reduced RANKL expression levels in vitro. Treatment of BMCs and MC3T3 with OPN also resulted in increased ERK phosphorylation and reduced OPG levels. Together, our studies suggest that increased OPN expression during unloading-induced drifting of teeth enhances localized RANKL expression and osteoclast activity on drift-direction alveolar bone surfaces via extracellular matrix signaling pathways.

Rotational drift of mandibular third molar teeth: a series of four cases.

Rotational drift of mandibular third molar teeth is a challenge for clinicians to predict and manage. Evidence on the incidence and degree of rotation is sparse. As the factors influencing rotation are not defined, prediction is impossible. A series of four cases with lower third molar rotation are presented and discussed. Significant rotation can alter the degree of difficulty for an extraction. A lack of well-documented cases has hindered investigation of this phenomenon. Further research is required to identify the aetiology, incidence and increase in risk factors caused by such rotational drift.

Natural frequency analysis of tooth stability under various simulated types and degrees of alveolar vertical bone loss.

The aim of this study was to test natural teeth stability under various simulated types and degrees of alveolar vertical bone loss, as well as to assess the role that the surrounding bone played for maintaining tooth stability. A three-dimensional finite element model of the human maxillary central incisor with surrounding tissue, including periodontal ligament, enamel, dentin, pulp, and alveolar bone, was established. One side and multiple vertical bone loss were simulated by means of decreasing the surrounding bone level apically from the cemento-enamel junction in 1 mm steps incrementally downward for 10 mm. Natural frequency values of the incisor model with various types and degrees of bone loss were then calculated. The results showed that, with one-sided bone resorption, the model with labial bone loss had the lowest natural frequency decreasing rates (8.2 per cent). On the other hand, in cases of multiple bone loss, vertical bone resorption at the mesial and distal sides had more negative effects on tooth stability compared to vertical bone losses on facial and lingual sides. These findings suggest that the natural frequency method may be a useful, auxiliary clinical tool for diagnosis of vertical periodontal diseases.

Mechanisms of tooth eruption and orthodontic tooth movement.

Teeth move through alveolar bone, whether through the normal process of tooth eruption or by strains generated by orthodontic appliances. Both eruption and orthodontics accomplish this feat through similar fundamental biological processes, osteoclastogenesis and osteogenesis, but there are differences that make their mechanisms unique. A better appreciation of the molecular and cellular events that regulate osteoclastogenesis and osteogenesis in eruption and orthodontics is not only central to our understanding of how these processes occur, but also is needed for ultimate development of the means to control them. Possible future studies in these areas are also discussed, with particular emphasis on translation of fundamental knowledge to improve dental treatments.

Occlusal changes following posterior tooth loss in adults. Part 3. A study of clinical parameters associated with the presence of occlusal interferences following posterior tooth loss.

PURPOSE: Tooth positional changes following posterior tooth loss may alter arch forms and occlusal planes. This may result in the development of occlusal interferences. The purpose of this study was to determine clinical parameters associated with the presence of retruded contact position (RCP) contacts and occlusal interferences associated with posterior tooth loss. MATERIALS AND METHODS: Diagnostic casts of 100 patients with at least one unopposed posterior tooth and 100 control patients were scanned and analyzed to record clinical parameters described in the earlier publications in this series. Clinical examinations identified the presence of RCP contacts and occlusal interferences. Five generalized linear models were developed to investigate the parameters associated with presence of RCP contacts, protrusive interferences, working side interferences, and nonworking side interferences. RESULTS: RCP contacts were associated with the degree of supraeruption of the unopposed tooth and the presence of other types of interferences. Protrusive interferences were associated with the presence and position of a tooth distal to the extraction site and the presence of other types of interference. Working side interferences were associated with tipping of the tooth mesial to the extraction site and the presence of other interferences. Nonworking side interferences were associated with the presence of other types of interference only. CONCLUSION: Unopposed posterior teeth are more likely to be involved in RCP contacts or interferences than their matched controls. Many teeth were involved in multiple interferences, and there appears to be a number of interrelationships between these. Initial RCP contacts have associations with the extent of supraeruption of the unopposed teeth. The presence and position of the teeth distal to extraction sites was significant when modeling protrusive interferences. Protrusive interferences are more prevalent where the site of tooth loss was bounded. Mesial tipping of the teeth distal to extraction sites reduced this effect. Working side interferences were associated with tipping of teeth mesial to the site of tooth loss. No associations between patient or tooth factors were found for nonworking side interferences, and the only association found for these interferences were with protrusive interferences at the sites.

Patterns of intraosseous transmigration and ectopic eruption of bilaterally transmigrating mandibular canines: radiographic study and proposed classification.

Unilateral transmigration of mandibular canines is a rare phenomenon. Occurrence of bilateral transmigration of mandibular canines is even more rare. There are diagnostic, therapeutic, and prognostic implications in the occurrence of these transmigratory patterns. Proper understanding of the mechanisms involved in the impaction and intra-osseous movement of these teeth within the bone will help clinicians to intervene and formulate better treatment options. A review of previously reported cases of bilaterally transmigrating mandibular canines from the literature was undertaken. Five new cases are reported in this article. Classification of the bilaterally transmigrating mandibular canines is proposed for better understanding, ease of communication, and appropriate management of this aberrant migratory pattern.

A review of the shortened dental arch concept focusing on the work by the Käyser/Nijmegen group.

The aims of this paper were to review the literature on shortened dental arches with special focus on publications of the Käyser/Nijmegen group, and to evaluate the discussions on the shortened dental arch concept found in the literature. A MEDLINE (PubMed) search was conducted for articles in English published in the dental literature from 1966 to November 2005. The search revealed epidemiological, cross-sectional and longitudinal clinical studies as well as opinion papers, the majority of which were published by the Dutch group. The studies found in general no clinically significant differences between subjects with shortened dental arches of three to five occlusal units and complete dental arches regarding variables such as masticatory ability, signs and symptoms of temporomandibular disorders, migration of remaining teeth, periodontal support, and oral comfort. The findings from cross-sectional studies were corroborated longitudinally. No systematic clinical study with conflicting results was found. The shortened dental arch concept was accepted by a great majority of dentists but not widely practised. The studies reviewed showed that shortened dental arches comprising anterior and premolar teeth in general fulfil the requirements of a functional dentition. It may therefore be concluded that the concept deserves serious consideration in treatment planning for partially edentulous patients. However, with ongoing changes, e.g. in dental health and economy, the concept requires continuing research, evaluation and discussion. Patients' needs and demands vary much and should be individually assessed but the shortened dental arch concept deserves to be included in all treatment planning for partially edentulous patients.